The present invention relates to ventilator apparatus, and particularly to portable ventilator apparatus useful for providing mechanical ventilation of a patient at home or during transport.
Ventilating apparatus is widely used for mechanically forcing air into the lungs of a patient requiring ventilatory assistance. Some ventilators are designed for continuous use in hospitals, such as in intensive care units; and others are designed as portable units for use in the home or during transport. Examples of the latter are described in U.S. Pat. Nos. 3,499,601, 4,215,681 and 4,493,614. The present invention is particularly applicable to ventilators of the portable type for use in the home or during transport.
Ventilators are usually also divided into the following types:
1. Pressure ventilators, usually including a source of compressed air administered by a solenoid valve at a rate of 10-30 breaths per minute. Such ventilators usually include large-size pistons (e.g., 10-12 inch diameters) having sealing surfaces with respect to the cylinders in which they move, and in general are characterized by bulky construction precluding portability, high power consumption because of continuous operation precluding the use of batteries, and/or poor control of the volume the patient inhales with each breath.
2. Volume ventilators, usually including a large reciprocating piston driven by an electric motor for compressing air into the patient's lungs at a preset fixed volume with the cycling frequency varying from 5 to 40 breaths per minute. Such ventilators are generally characterized by inability to attain high frequencies required for baby respiration, poor control of the volumes when they are set very low since the piston stroke becomes very critical, and/or poor mechanical efficiency since most of the energy is expended in overcoming friction in the piston seal and in the transmission from the motor to the piston.
3. Continuous positive airway pressure (CPAP) ventilators, usually including a compressor providing continuous positive pressure at a low pressure level. Such ventilators are usually used only for applying a positive pressure to the patient's lungs in order to help alleviate obstructive apnea during sleep while the patient breathes against the continuous pressure.
4. High-frequency positive-pressure ventilators, in which a source of compressed air is controlled to deliver air to the patient at controlled volumes and at rates between 60 and 120 breaths per minute. Such ventilators are usually of bulky construction and therefore are primarily used in clinical applications.
5. High-frequency jet ventilators, which include compressors delivering high pressure air directly to the lungs at frequencies of up to 400 cycles per minute.
6. High-frequency oscillation ventilators, which include compressors delivering very small volumes of pressurized air to the lungs at frequencies of up to 2400 cycles per minute.
My prior application Ser. No. 07/071,327 discloses ventilator apparatus which may be embodied in a compact, portable construction and which can substantially duplicate the performance of all six types of ventilators described above.
The present application is directed particularly to ventilators of the CPAP (continuous positive airway pressure) type (Type 3 above) for helping to alleviate obstructive apnea during sleep.
The presently used CPAP ventilators generally include small turbines, such as vacuum cleaner turbines, generating high air flow rates with low pressure. They also include a relief valve, commonly called a "PEEP" (Positive End Expiratory Pressure) valve which releases the pressure to the atmosphere when the pressure in the delivery conduit rises above a predetermined value. However, such known CPAP ventilators are usually characterized by the following shortcomings: (1) they are noisy; (2) they are wasteful of power, since they generate an air flow which is not only far in access of the patient's needs to guarantee sufficient flow for all patients under various conditions, but they also generate air flow while the patient is exhaling; (3) they are wasteful of oxygen when applied to the delivered air, since the oxygen is included with the continuously supplied air; and (4) for the same reasons, they are also wasteful of moisture when a humidifier is used to humidify the delivered air.
An object of the invention in the present application is to provide a ventilator apparatus of the type described in Application Ser. No. 07/071,327, designed particularly to be used as a CPAP ventilator but not subject to the above drawbacks of the existing ventilators of this type.